1. Field of the Invention
The present invention relates to a procedure whereby fatty acids found in various oils, such as for instance, tall oil and soybean oil, are polymerized so as to obtain a mixture rich in dimeric and trimeric fatty acids. More particularly, it relates to a method for polymerizing unsaturated fatty acids, utilizing stepwise catalytic reactions.
2. Brief Description of the Prior Art
It is well known that monomeric unsaturated fatty acids which are derived from natural sources are capable of being polymerized to the dimerized and trimerized form. This is usually realized by heating such unsaturated fatty acids in the presence of catalytic proportions of a mineral clay and, preferably, an acid-treated mineral clay, at temperatures in excess of about 180.degree. C. in an aqueous environment under autogenous pressure. Small amounts of water are deemed necessary for reaction to minimize the degradation of the fatty acids being treated. Representative of the prior art teachings are those found in the U.S. Pat. Nos. 2,793,219 and 2,793,220.
The U.S. Pat. No. 3,422,124 describes an improvement over the above-described prior art processes in that higher overall yields of the desired dimer and trimer products could be obtained by a two stage heating process. As explained in the U.S. Pat. No. 3,422,124, after a polymerization, which may yield around 60 percent polymeric species, the residual monomeric acids are unpolymerizable. However, the patentees discovered that if the initial polymerization were carried out under anhydrous conditions and in the presence of (a) glacial acetic acid, anhydrous propionic acid or anhydrous butyric acid, (b) an acid-treated mineral clay catalyst and (c) unsaturated fatty acids, then residual monomeric fatty acids could be polymerized in a second, conventional polymerization stage. This, of course, improved overall yields of dimer and trimer.
The two-stage polymerization was also used in the process disclosed in U.S. Pat. No. 3,632,822, which does not require the anhydrous and acid conditions recited in the U.S. Pat. No. 3,422,124. The patentee of the U.S. Pat. No. 3,632,822 revealed that those conditions were not required if one employed as the catalyst an acid-activated clay modified with an alkaline earth metal salt such as calcium chloride.
The process of the present invention is yet another improvement over the prior art processes. By the employment of an unactivated clay catalyst in a two-stage polymerization it has been found that still improved overall yields of dimer and trimer product may be achieved. The elimination of the need for an acid-activated clay catalyst has obvious advantages. Still further the dimer-trimer products have light colors and low viscosities, i.e., less than 10000 Cst @ 25.degree. C. Other advantages of the process of the invention will be described hereinafter.